The invention relates to a geodesic positioning system for determining the position of a target point with the aid of a range pole that can be oriented toward the target point.
Such a positioning system is for instance known from U.S. Pat. No. 5,512,905 A. A range pole system is described that involves a range pole that can be positioned on a target point situated more particularly on the ground, and is fitted at its upper end with a positioning element that may have the form of a reflector or satellite signal antenna. In addition, a biaxial tilt sensor that detects the tilt angle of the range pole, and a directional sensor, more particularly a compass, that detects the azimuthal orientation of the biaxial tilt sensor are attached to the range pole. The position of the target point is determined vectorially from a knowledge of the positioning element's position as determined by means of a tachymeter or of satellite signals, from the range pole's tilt angle, from the azimuthal orientation of the biaxial tilt sensor, and from the range pole's length. The vertical alignment of the range pole that is required in conventional systems may thus be omitted. However, the requirement of knowing the azimuthal orientation of the range pole is a disadvantage of the system described. This orientation cannot be determined with a single satellite signal antenna, so that a directional sensor must be employed, primarily a costly magnetic compass system or a demanding satellite positioning system involving several antennas. However, such systems have limited applicability in geodesy, inasmuch as they are complex, interference-prone, and not accurate enough for geodesic purposes, and will not function in places with interfering magnetic fields, more particularly in the vicinity of ferromagnetic objects, nor in shaded areas. A positioning accuracy of better than one to two centimeters cannot be attained with the system described.
In the U.S. Pat. No. 6,067,046 A, a geodesic positioning system involving a range pole is described that carries a GPS antenna and a spherical or tubular level. By reading the level, a user orients the range pole so that it will vertically point to a target point on the ground. The user triggers acquisition of the current GPS value by pushing a button as soon as he estimates that the orientation of the range pole is sufficiently vertical. However, this classical procedure has essential drawbacks. A decision as to whether the range pole is vertically aligned is made by the user, and thus is purely subjective, and may produce differing results. In addition, a sole value is acquired, that may correspond to the position just determined by the GPS antenna or to a mean of positions determined within a period of time prior to triggering the acquisition, and possibly with alignments of the range pole out of the vertical. In both cases a faulty determination cannot be excluded.
In the U.S. Pat. No. 5,929,807 A, a procedure and a device for positioning with the aid of a GPS range pole are proposed where neither a tilt sensor nor a directional sensor is needed. The GPS range pole is placed on a target point with one end, and then swayed by the surveyor around this target point while maintaining the contact between said end of the range pole and the target point. While the range pole is swayed, a multitude of positional points are acquired by means of the GPS antenna mounted onto the other end of the range pole. As said other end of the range pole is moved about a virtual spherical surface while being swayed, the acquired positional points will also be situated on a virtual spherical surface having the target point as its center, so that from the multitude of acquired positional points one may deduce the target point about which the range pole is swayed, by using calculus, for instance a mathematical least-squares analysis. However, if one wants to position the target point highly accurately for geodesic purposes, it will be necessary to determine the positional points highly accurately in all three coordinates, while satellite positioning systems offer limited possibilities for doing so, inasmuch as in said systems inherently the vertical positioning accuracy is substantially lower than the horizontal one. A sway of the range pole involving a tilt angle of about 20 degrees produces a vertical positioning accuracy of merely about three to four centimeters. For a determination of the sphere's center, and thus the target point, with an accuracy of better than one centimeter, the sway ought to occur with a sway angle of 90° when using a range pole having the usual length of about two meters, so that a hemisphere would be described. This is hardly realistic, already for ergonomic reasons, so that a positioning accuracy of better than one centimeter is not possible with the procedure described.
A solution to this problem is proposed in US 2003/0,058,164 A1, where in addition a tilt sensor is attached to the range pole, and the positional points acquired while swaying are each associated with the corresponding tilt angle of the range pole. The additional quantity gained in this way allows a higher positioning accuracy to be attained.
In JP 2002/022,443, a procedure is described that essentially corresponds to that of U.S. Pat. No. 5,929,807 A. However, instead of a GPS antenna, a reflector pointable by a tachymeter is used as the positioning element.
The procedures and devices described in U.S. Pat. No. 5,929,807 A, US 2003/0,058,164 A1, and JP 2002/022,443 have the common drawback that a great many individual measurements must be performed, and that the computational determination of the target point that is based on said multitude of data must be done by a costly calculation. On the one hand, this is time-consuming and ergonomically unfavorable, inasmuch as the range pole must be swayed about by the surveyor during a certain period of time. On the other hand, the evaluation requires high computing capacities. For real-time measurements, the procedures described require a manipulation of the unit used to evaluate the positional data, for instance of the GPS or tachymeter evaluating unit, or a demanding data postprocessing, since the position of the target point cannot be determined without demanding mathematical operations from the positional data acquired for the positioning element, and more particularly the GPS antenna or the reflector. Problems arise above all in modular systems where different modules are employed for a variety of measurements in a variety of configurations.
It is the aim of the invention to provide a highly precise modular geodesic range-pole positioning system for determining the position of a target point that has a favorable ergonomic operation, simple structure, and economic implementation, and that may as well be operated when an interference-free terrestrial magnetic field is not available, while essentially avoiding spurious results; and to improve the range-pole positioning systems known from the prior art.
This aim is achieved by realizing the characterizing features of the independent claim. Features developing the invention in an alternative or advantageous way can be seen from the dependent claims.